1. Field of the Invention
The present invention relates to a DC motor drive and, more particularly, to a DC motor drive with a combination step control practical for use in an electric steel rolling door or the like.
2. Description of the Related Art
FIG. 1 shows a motor drive for use in an electric steel rolling door according to the prior art. As illustrated, the motor drive comprises a DC motor 1xe2x80x2, a control mechanism 2xe2x80x2, and a clutch 3xe2x80x2. The DC motor 1xe2x80x2 is adapted to roll up/let off the steel rolling door. The control mechanism 2xe2x80x2 is comprised of a limit switch 22xe2x80x2 and two control rods 21xe2x80x2, and adapted to control the direction of rotation of the DC motor 1xe2x80x2. The clutch 3xe2x80x2 has a handle 31xe2x80x2 for operation by hand to disengage a clutch gear from the DC motor 1xe2x80x2 for enabling the DC motor 1xe2x80x2 to run idle when AC power failed. This design of motor drive is expensive to manufacture. Further, installation and maintenance works of this design of motor drive are complicated.
The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a motor drive, which combines a DC motor, step counting means, and clutch means into a simple compact structure. It is another object of the present invention to provide a motor drive, which is inexpensive to manufacture and easy to maintain. To achieve these and other objects of the present invention, the motor drive comprises a DC motor, the DC motor having a casing at one side and a worm fixedly mounted on an output shaft thereof and fastened pivotally with the casing; a speed reducing mechanism, the speed reducing mechanism comprising a main shaft fastened pivotally with the casing, and a worm gear mounted on the main shaft for free rotation relative to the main shaft and meshed with the worn, the worm gear having a plurality of radial engagement blocks equiangularly located on one side thereof; a clutch mounted inside the casing, the clutch comprising a clutch gear, the clutch gear axially movably mounted on the main shaft of the speed reducing mechanism, an annular flange protruded from an opposite side thereof, and a locating groove extended around the periphery of the annular flange, the clutch gear being axially movable along the main shaft relative to the worm gear between a first position where the clutch gear is forced into engagement with the radial engagement blocks of the worm gear for enabling synchronously rotation with the worm gear, and a second position where the clutch gear is disengaged from the radial engagement blocks of the worm gear for enabling idle running, a spring member adapted to force the clutch gear into engagement with the worm gear, a lever coupled to the locating groove of the clutch gear, and a locking plate coupled to the lever for operation by the user to drive the lever to move the clutch gear away from the worm gear for enabling the main shaft to run idle; a mechanical step counter adapted to control forward/backward rotation of the DC motor, the mechanical step counter comprising a limit switch, a first reducing gear set coupled to the main shaft for synchronous rotation and adapted to drive the limit switch to control forward rotation of the DC motor, and a second reducing gear set coupled to the main shaft for synchronous rotation and adapted to drive the limit switch to control backward rotation of the DC motor, the first reducing gear set and the second reducing gear set each having a last reducing gear, the last reducing gear having a gear shaft extending out of one sidewall of the casing, and a protruding block mounted on the gear shaft of said last reducing gear and adapted to trigger a respective contact of the limit switch; and an electronic step counter, the electronic step counter comprising a control IC, a multi-magnet member mounted on one end of the worm for synchronous rotation, and an inductor fixedly mounted in the casing and facing the multi-magnet member and adapted to detect the pulse of the DC motor and output a signal to he control IC subject to the pulse of the DC motor, enabling the control IC to calculate the time to control forward/backward station of the DC motor.